In multi-phase electronic converter applications, a number of bridge driver circuits (full or half) can be cascaded together while sharing a common power supply 110. A full bridge converter 100 is shown in FIG. 1 with four actuators (120) cascaded together. In this design, each load element 120 (actuator) is independently controlled by modulating the conduction of the appropriate power devices, in one of the three voltage operating modes (positive voltage, negative voltage, free-wheeling mode) by actuating switches 112 and 118, 114 and 116, 112 and 116 or 114 and 118, respectively. Note also that a half-bridge configuration can also be used for applications that do not require bi-directional current flow (where the power switches (114 and 116) are replaced with power diodes).
However, the inventors herein have recognized a disadvantage when trying to use such converter designs to control electromechanically actuated valves of a cylinder in an internal combustion engine. For example, a full bridge converter can require four power devices (4 switches) for each electromagnet. And, since electrically actuated valves of an engine typically use two actuator coils per cylinder, a typical 32 valve V-8 engine would require 256 devices. This creates a significant added cost for an engine with electromechanically actuated valves, even if not all valves are electrically powered. Further, not only would the above converter approaches require significant numbers of devices, but would also increase wiring and harness costs, since two wires are required per actuator coil.
As another example, in the case of a half bridge converter, when used with actuators having embedded permanent magnets, improved operation may be obtained using bi-directional current. However, such a converter may not provide such operation, and therefore may lose the advantage of having permanent magnet enhancements. Further, such a converter may still require 4 power devices (2 switches and 2 diodes) per electromagnet.
The above disadvantages can be overcome by an electronic circuit, comprising:
a first electromechanical actuator coil coupled to one of a plurality of cylinder valves of an internal combustion engine, where a first end of said first electromechanical actuator coil is coupled to a reference;
a second electromechanical actuator coil, where a first end of said first electromechanical actuator coil is coupled to said reference;
a first energy storage device, where a first end of said first energy storage device is coupled to said reference;
a second energy storage device, where a first end of said second energy storage device is coupled to said reference;
a first switch, where a first end of said first switch is coupled to a second end of said first electromechanical actuator coil; and
a second switch, where a first end of said second switch is coupled to said second end of said second electromechanical actuator coil.
In this way, it is possible to obtain bi-directional current control while still offering a reduction in device count and wire count. Thus, it may be possible to provide improved cost, reduced complexity, and reduced packaging space.